If the "unissued" M5A1 comes with a new (or even "like-new") M8A1 scabbard, then $60 is not a bad price at all.
A new production M7 bayonet (M4/M16) with the ****** plastic M10 scabbard can go for as much as $40-$50 depending on where you get it.
The M5A1 is generally more desireable than the M7, even though they are both variants of the
same bayonet, and the scabbards are a bonus. Some of my M8A1 scabbards are worth more than the bayonets in them!
Okay, so its not a Garand, but I just can't resist a little bayo porn...